Regenerative fuel pumps have been widely used in automotive applications because of the low specific speed number (ratio of diameter and flow rate versus pressure), quiet operation, good handling of hot fuel, and durability. These regenerative fuel pumps generally include an impeller rotating on a shaft and positioned within an impeller chamber in the pump. The clearance between the opposing axial sides of the impeller and the corresponding walls of the impeller chamber must be closely regulated to permit the pump to handle fuel at relatively high pressures (i.e. greater than about 2 bar). The impellers are typically double sided impellers, meaning the impellers include vanes on each opposing side which have vanes positioned therein for pressurizing fuel on both sides of the impeller. In this manner, the impellers are relatively well balanced axially to maintain the necessary clearance for pumping high pressure fuel.
One drawback of these fuel pumps is that their wet circle index is relatively high, typically 1.7 or greater. The wet circle index is an index for the pump boundary layer and friction losses. The wet circle index can be defined as the wet circle length versus the flow channel cross-sectional area. That is, the wet circle length is the distance along the perimeter of the flow channel (i.e. circumference of a round flow channel), the follow channel being formed by both the impeller and the structures (e.g. body and cover structures) on opposing sides of the impeller.
Another problem with these types of fuel pumps is that as the fuel is pressurized, back pressure builds up within the pumping chamber causing backflow leakage which reduces the efficiency of the pump.
Accordingly, there exist a need for a fuel pump with robust axial clearance requirements to permit pumping of high pressure fluid in an automotive environment, while at the same time having a lower wet circle index to reduce friction losses and improve the efficiency of the pump while providing a more gradual pressure increase of the fuel to lessen back pressure within the fuel pump.